This invention relates to a liquid level control device. In particular, it relates to a control head on the device which can be changed from the snap-actor mode to the throttling mode without removal or addition of any parts.
It has been known in the art to provide a control head on a liquid level control device which has both a snap-actor and throttling mode of operation. An example of such a device is shown in pending U.S. patent application Ser. No. 537,783 filed Sept. 30, 1983 which is commonly owned by the assignee of this application. Another example of such a device is shown in U.S. Pat. No. 3,840,044 issued Oct. 8, 1974 to Lewis K. Harris et al. Some other patents related to the invention are U.S. Pat. No. 2,649,771 issued Aug. 25, 1973 to A. S. Parks, U.S. Pat. No. 3,413,997 issued Dec. 3, 1968 to J. L. Taylor and U.S. Pat. No. 3,088,485 issued May 7, 1963 to A. J. Hanssen.
The above U.S. Pat. No. 3,840,044 and pending U.S. patent application Ser. No. 537,783 are incorporated herein in toto by specific reference thereto.
These snap-actor and throttling control heads are used in connection with liquid level control devices. The devices have particular uses as pneumatic liquid level controls. In particular, they may be used to control liquid levels in oil well pressure vessels. Oil and gas wells generally produce natural gas and a mixture of water and hydrocarbons. The pressure vessels separate the water from the hydrocarbons. Because the level of liquid in the pressure vessel cannot be allowed to vary much, a liquid level control device is needed which is sensitive to small changes in liquid level in the vessel. The natural gas produced can be used to open or close a gas actuated motor valve which drains or adds liquid to the vessel by flowing the gas through a liquid level control device and to a gas actuated motor valve, which in turn controls the liquid level, and the cycle is repeated. The device may also be used for many other types of liquid level control. Also, if sufficient gas is not present from the well, it may be supplied from an outside source to the device by compressed air or the like.
It is desirable that liquid level control devices be able to operate in all weather conditions. Because the gas used, particularly natural gas, may contain water vapor which will freeze if the ambient temperature falls below the dew point, it is necessary to provide a device which works in all temperature extremes. In temperatures above the dew point, a liquid level control device can operate in a "throttling mode". This mode keeps liquid at a constant level and allows liquid to be drained gradually from the vessel. Gas flow through the device to the gas operated motor valve at a variety of volumes depending on the level of liquid in the vessel. The gas flow is constantly choked to some degree at a small orifice. However, if water vapor in the gas flowing through the control device starts to freeze, ice or condensate may be built up on the small orifices used in the throttling mode and cause liquid level upsets in the vessel. In this situation, a device which operates in a "snap-actor" mode is preferable.
The snap actor mode allows the liquid level in the vessel to be controlled between predetermined limits by nozzle adjustment in relation to float position. Some fluctuation in liquid level is tolerable. Fluctuation of the liquid level produces either full supply gas pressure to the liquid level control device, which causes the drain valve controlled by the device to open to its fullest open position and drain the vessel, or no supply gas pressure because the supply gas is completely vented from the liquid level control device, which causes the vessel drain valve to fully close. The time interval between these operations provides a warming interval for the control device to dissipate any forming of ice at the orifices. Also, when gas flows through the control device during the full open position of the liquid level control device, the gas pathway through the device uses larger flow orifices than those used in the throttling mode so that blockage due to icing is reduced.
While other devices have been known which are capable of shifting between a snap-actor mode and a throttling mode, none has achieved the shift in modes with the simplicity and ease of operation of the present invention. In particular, in U.S. patent application Ser. No. 537,783, one must put in a pipe plug such as plug 84 shown in FIG. 1 of said pending application and must switch the control screws by opening one and closing another. In order to achieve this function with U.S. Pat. No. 3,840,044, it is necessary to remove and switch certain components. In the field, this may create problems in the event small parts are dropped or lost.
It is an object of the present invention to provide a control head for a liquid level control device which may be changed from the snap-actor mode to the throttling mode without dismantling the device or adding any additional elements. In particular, it is an object of the invention to provide a control head which may be easily converted from one mode to another by merely loosening the booster head assembly from the control assembly and rotating it between two preselected positions. It is another object of the invention to provide a device which may be switched between the two operating modes without adding any additional elements. It is another object of the invention to provide a device which can be switched between two modes without dismantling or removing any parts from the device. It is also another object of the invention to provide a device which can be quickly changed between the two operating modes with common tools such as a screwdriver. Other objects of the invention will become apparent from the following detailed disclosure.